Phenolic compounds are basic chemicals of high interest to the chemical and pharmaceutical industries. Phenolic compounds are important plant constituents and phenol is formed from a variety of natural and synthetic substrates by the activity of microorganisms. The aerobic metabolism of phenol has been studied extensively; in all aerobic metabolic pathways oxygenases initiate the degradation of phenol by hydroxylation to catechol. Catechol can be oxygenolytically cleaved by dioxygenases, either by ortho- or meta-cleavage.
Anaerobic metabolism of phenol, aniline, o-cresol (2-methylphenol), hydroquinone (1,4-dihydroxybenzene), catechol (1,2-dihydroxybenzene), naphthalene and phenanthrene (Zhang et al., App. Environ. Microbiol. 63:4759-4764 (1997)) by denitrifying and sulfate-reducing bacteria involves carboxylation of the aromatic ring ortho orpara to the hydroxy or amino substituent. Products are 4-hydroxybenzoate, 4-aminobenzoate, 4-hydroxy-3-methylbenzoate, gentisate (2,5-dihydroxybenzoate), and protocatechuate (3,4-dihydroxybenzoate) (Heider et al., Eur. J. Biochem. 243:577-596 (1997)). Consortia of fermenting bacteria convert phenol to benzoate and decarboxylate 4-hydroxybenzoate to phenol (Winter et al., Appl. Microbiol. Biotechnol. 25:384-391 (1987); He et al., Eur. J. Biochem. 229:77-82 (1995); He et al., J. Bacteriol. 178:3539-3543 (1996); Van Schie et al., Appl. Environ. Microbiol. 64:2432-2438 (1998)). They also catalyze an isotope exchange between D.sub.2 O and the proton at C4 of the aromatic ring of 4-hydroxybenzoate. Phenol carboxylation to 4-hydroxybenzoate in the denitritying bacterium Thauera aromatica is the best studied of these carboxylation reactions and is a paradigm for this new type of carboxylation reaction (Tschech et al., Arch. Microbiol. 148:213-217 (1987); Lack et al., Eur. J. Biochem. 197:473-479 (1991); Lack et al., J. Bacteriol. 174:3629-3636 (1992); Lack et al., Arch. Microbiol. 161:132-139 (1994)).
Without an isolated gene and corresponding sequence of the coding sequence, there remains a need for a convenient way to produce various intermediates in phenol metabolism with a transformed microorganism.